Excimer laser unit and relative control method for performing cornea ablation to reduce presbyopia

Abstract

There are described an excimer laser unit and a method of controlling the unit to perform cornea ablation to reduce presbyopia, wherein the excimer laser unit is controlled to form on the cornea a photoablative pattern inducing a fourth-order ocular aberration, in particular a positive spherical aberration. More specifically, an aberrometric map of the eye is first acquired indicating the visual defects of the eye, which include second-order visual defects such as hypermetropia, astigmatism, and myopia, and higher-order visual defects such as spherical aberration; if the detected spherical aberration is negative, it is reduced by numerically increasing its absolute value to obtain an overcorrect photoablative inducing positive spherical aberration; conversely, if the detected spherical aberration is positive, its sign is changed and its absolute value increased numerically to obtain an overcorrect photoablative pattern inducing positive spherical aberration; and the photoablative pattern so generated is supplied to the excimer laser unit for implementation on the cornea.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS [0001] This application claims priority of International Application No. PCT / IT 2003 / 000747, filed Nov. 18, 2003 and Italian Application No. TO 2002A001007, filed Nov. 19, 2002, the complete disclosures of which are hereby incorporated by reference.TECHNICAL FIELD [0002] The present invention relates to an excimer laser unit and relative control method for performing cornea ablation to reduce presbyopia. BACKGROUND ART [0003] As is known, the human eye can be likened to a camera, in which the lens is defined by two lenses in turn defined by the cornea and the crystalline lens, the diaphragm by the pupil, and the film by the retina. [0004] The lens focuses the rays from the outside world on the retina; the diaphragm expands and contracts to allow enough light into the eye to permit optimum operation of the retina with no glare phenomena; and the photosensitive film, defined by the retina, converts the light energy impressed on it into a visual ...

AI Technical Summary

Benefits of technology

[0122] It is a primary object of the present invention to provide an excimer laser unit and relative control method for performing cornea ablation to reduce presbyopia.

[0123] According to the present invention, there is provided a method of controlling an excimer laser unit to perform cornea ablation to reduce presbyopia.

Problems solved by technology

Myopia, astigmatism, and hypermetropia are defects of the optical system which result in the image not being focused correctly on the retina.

Theoretically, an increase in fluence improves the quality of the beam, but also increases the heat effect and acoustic shock, and produces more rapid wear of the optical components of the laser.

A non-homogeneous laser beam profile results in non-uniform ablation.

In this defect, rays from an infinite distance are focused behind the retina, on account of the poor vertex power of the eye with respect to its length.

It is essential not to induce a post-treatment increase in central curvature of over 50 diopters, which would result in a central keratoconus, with associated visual and central reepithelialization problems.

Presbyopia, on the other hand, is a visual defect which consists in diminished accommodation power of the eye to focus on near objects, is mainly encountered in adults, and is due to a loss of elasticity of the crystalline lens.

Unlike myopia, hypermetropia and astigmatism, presbyopia is therefore not a refractive defect and, unlike the cases described above, is not easy to solve using photoablative techniques.

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